With Team Japan, he holds the Asian Record for the 4 × 100 m freestyle relay (short course).

He was placed seventh in 53.93, much slower than his National record of 53.10 (which would have won him a silver medal.

[10]) On day five, after qualifying for the final, Hagino won another silver medal in the 200 m individual medley.

On the final night of competition, despite being the favorite, Hagino was only able to manage fifth place, finishing in 4:10.77.

On day one of the Pan Pacs in Gold Coast, Hagino swam in the 200m freestyle.

[14] Hagino later swam in the 4 × 200 m freestyle relay as the lead, clocking 1:46.13, touching first for Japan in the first leg.

On day four and Hagino's final event, he swam in the 200m individual medley that featured a competitive field including teammate Seto and American legends Michael Phelps, Ryan Lochte and Tyler Clary.

He again swam fastest in the 'A' final, swimming 1:56.62, narrowly out-touching Phelps by two hundredths of a second.

In the final, Hagino shaved off more than two seconds off his heats timing, swimming 1:45.23 for his first gold medal of the Games.

Hagino later swam in the 4 × 200 m freestyle relay, which Japan held the Asian Record of 7:02.26.

[24] On day five and Hagino's final event, he swam in the 200m backstroke, and qualified fourth in the heats with 2:00.34.

[35][36] Hagino won silver in the 200 m individual medley,[37] becoming the first Asian man (along with Wang Shun) to medal at the event,[38] and bronze in the 4 × 200 m freestyle relay.

[39] Hagino decided not to defend his 400 m individual medley title at the 2020 Olympics held in Tokyo in 2021.

On 24 Aug 2021, it was reported that he has informed his team of his decision to retire and is contemplating attending graduate school.